The present invention relates to a toolhead for multi-axis machine tools.
The invention finds application in systems able to perform drilling, countersinking or other such machining operations automatically and to extremely close tolerances, in situations where the exact height of the machined surface is not known.
In particular, whilst implying no limitation of its general scope, the invention can be associated to advantage with numerically controlled multi-axis machine tools as used especially in the aircraft industry for drilling and countersinking holes in the outer panels of wing structures and fuselage sections, in readiness for the insertion of rivets. In practice, the heads of the inserted rivets must remain perfectly flush with the outer skin of the aircraft in order to ensure they will not generate turbulence, which would occasion a marked increase in aerodynamic resistance.
The prior art embraces devices able to control drilling or countersinking depth, which are set up by performing a mechanical adjustment before each machining job.
Patent IT 1220732, in particular, discloses a depth-controlled drilling and countersinking device able to operate on surfaces positioned at any given height relative to the feed direction of the tool. The device in question comprises a tool-holder with a shank that can be attached to the spindle of a machine tool, also a stop cage mechanism associated with the tool-holder by way of a pair of bearings and presenting a pair of cylinders with piston rods that project from both ends. Each of the rods is connected at one end to a collar, through which the tool is insertable when penetrating the work, and at the opposite end to a mounting plate. The collar is translatable relative to the tool-holder, in a direction parallel to the tool axis. The mounting plate associated with the ends of the rods remote from the tool carries respective micrometer screws that can be locked fast in a selected position by means of stops. Two microswitches are fixed to the spindlehead, their axes coinciding with those of the two micrometer screws. The microswitches are also connected to suitable devices serving to pilot the tool feed movement of the spindle. To control the depth of the countersink, the position of the screws is adjusted in such a way that the distance between the tip of the screw and the corresponding microswitch is equal to the distance between the face of the collar and the tool, plus the depth of the countersink. During operation, the spindle of the machine continues to advance until the screws engage and trip the microswitches. At this point, the devices piloting the movement of the spindle will be caused by the resulting contact to retract the tool. The machining depth is thus mechanically controlled, and the switches serve simply to halt the movement of the spindle once the prescribed depth has been reached.
The applicant finds that prior art devices of the type outlined above could be improved from various standpoints.
More exactly, mechanically controlled devices of familiar type such as the one described above do not allow any automatic adjustment of the depth to which the tool is sunk during the work cycle.
In practice however, an adjustment of this kind becomes necessary given that, whilst the shanks of the rivets utilized are generally identical, the dimensions of the respective heads will often vary. Accordingly, the single tool by which the hole is first drilled and then countersunk must penetrate to different depths according to the size of the rivet head that will ultimately occupy the hole. Furthermore, it may be that the cycle will involve sinking all of the holes initially, with different diameters one from another, and then countersinking each one in turn with a single tool penetrating to different depths as determined by the diameters of the different holes.
To this end, when using devices of the prior art type, the machine must always be stopped so as to allow manual adjustment of the micrometer screws.
The object of the present invention is to resolve the problems encountered with prior art solutions by setting forth a toolhead for multi-axis machine tools that will allow of sinking and countersinking holes automatically to different depths without any mechanical adjustment of the tool being required.
A further object of the invention is to provide a toolhead for multi-axis machine tools designed so as to allow a reduction of the down times between machining cycles, thereby optimizing production.